Process for obtaining aluminum alloy conductors



United States Patent US. Cl. 14812.7 12 Claims ABSTRACT OF THE DISCLOSURE An improved process for the preparation of aluminum base alloy conductors wherein the alloy contains magnesium and silicon, which process includes the steps of holding the alloy at an elevated temperature, hot rolling to redraw rod with a specified cooling rate, cooling the redraw rod to room temperature, holding at an elevated temperature and cooling to room temperature at a specified rate.

This application is a continuation-in-part of US. patent application Ser. No. 496,148, filed Oct. 14, 1965, now abandoned for Process for Obtaining Aluminum Alloy Conductors, by Michael I. Pryor.

The present invention relates to an improved process for the manufacture of aluminum base alloys. More specifically, the present invention resides in a greatly improved process for the preparation of aluminum base alloys in wrought form, especially conductors, wherein the alloy contains magnesium and silicon.

The present invention relates specifically to heat treatable aluminum alloys in which the major portion of alloying elements are magnesium and silicon which will be principally in the form of the intermetallic compound magnesium silicide, Mg Si.

Alloys of this type are widely used for a variety of applications, including use in aluminum alloy conductors. For example, aluminum alloy 6201 is a high strength aluminum-magnesium-silicon alloy which in the heat treated condition shows a tensile strength of about 46,000 p.s.i. minimum, and elongation of 3% minimum and an electrical conductivity of 53.5% IACS minimum.

characteristically this alloy is manufactured commercially by DC casting, reheating to about 700 to 850 F., hot rolling to redraw rod, cold drawing, solutionizing at around 1000 F. for 1 hour or more followed by water quenching, additional cold drawing and artificial aging between 250 and 450 F. to specification properties.

Batch solutionizing is conventionally conducted on this alloy on relatively small, spaced coils of no more than 250 lbs. which must be carefully water quenched.

From a manufacturing point of view the solutionizing of drawn, intermediate diameter wire is an expensive and slow process. It is particularly difficult because of the quench sensitivity of this alloy. In fact, the entire foregoing operation adds substantially to the manufacturing cost of conductors of this type.

It is highly desirable to make this intermediate diameter resolutionizing operation a continuous process. If this could be done, significant manufacturing economies would result. In addition, batch processing frequently results in hard spots in the resultant product and irreproducibility from length to length. Continuous processing would tend to eliminate these disadvantages. Indeed, if the entire resolutionizing process could be eliminated, even greater economies would result with the overall processing more closely approximating that of conventional electrical grade aluminum.

3,464,866 Patented Sept. 2, 1969 Accordingly, it is a principal object of the present invention to provide an improved process for the preparation of aluminum-magnesium-silicon alloys in wrought form, especially conductors.

It is a particular object of the present invention to provide a process as above which enables the attainment of good physical properties in the resultant article while achieving significantly reduced manufacturing cost.

It is a still further object of the present invention to provide a process as aforesaid which eliminates the entire resolutionizing operation while retaining excellent physical properties in the ultimate article.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily achieved.

The present invention comprises:

(A) Providing an aluminum base alloy containing from 0.20 to 1.3% silicon, from 0.3 to 1.4% magnesium, and the balance essentially aluminum;

(B) Holding said alloy at a temperature of from 850 to 1150" F. for at least 5 minutes;

(C) Hot rolling with a cooling rate during hot rolling of greater than F. per minute;

(D) Cooling to below 250 F., and preferably to room temperature, at a rate greater than 100 F. per minute with no more than 20 seconds delay between application of the cooling treatment and exiting of the last hot rollin g pass.

In the preferred embodiment when the process of the present invention is employed in the preparation of aluminum base alloy conductors, the alloy is hot rolled in step (C) to redraw rod, preferably having a diameter of about inch. In addition, the following steps are preferably employed subsequent to step (D):

(E) Cold drawing with at least 70% reduction in cross sectional area; and

(F) Heating at from 250 to 450 F. for at least 15 minutes.

The foregoing process significantly reduces the cost of the commercial preparation of aluminum base alloys in Wrought form, especially conductors. The process described above is readily susceptible to use on a continuous commercial scale and effects significant manufacturing economies. I

In accordance with the present invention, it has been discovered that by the use of the foregoing, carefully defined series of process steps substantial manufacturing economies are obtained and surprisingly the entire resolutionizing operation can be eliminated. Application of the foregoing hot rolling and cooling treatments adequately retains magnesium silicide in solution. In. accordance with conventional processing, the normal direct chill casting and conventional hot rolling provides the magnesium silicide in coarsely precipitated and widely distributed manner. This coarse precipitate requires long periods of time to redissolved. The coarse precipitate can be redissolved slowly by batch treatments and retained in solution by batch quenching. However, in batch quenching cooling rates and degree of retention are frequently non-uniform and the resultant product may have hard spots with irreproducible characteristics from length to length.

The present invention is utilizable with aluminum base alloys in wrought form, e.g., sheet and plate. Particularly advantageous is the preparation of plate of inch thickness and up. However, the preferred embodiment is aluminum base alloy conductors; hence, the ensuing discussion will be particularly related to this preferred emhodiment.

In accordance with the present invention the aluminum alloy may be conventionally cast in the customary manner. The cast bar is then completely solutionized by holding in the temperature range of 850 to 1150 F. for a period of time of at least 5 minutes and preferably at a temperature of 900 to 1050 F. for a period of time of between minutes and 16 hours.

After the foregoing homogenization step, the solutionized cast bar is hot rolled into redraw rod, conventionally having a diameter of about /8 of an inch. The solutionized bar is hot rolled to redraw rod so that during hot rolling the cooling rate is greater than 400 F. per minute. When sheet or plate is being utilized, the cooling rate should be greater than 100 F. per minute. By utilizing the foregoing hot rolling practice, the redraw rod existing from the hot rolling mill will be substantially free of precipitated magnesium silicide. The redraw rod is then cooled to below 250 F. and preferably to room temperature at a rate greater than 100 F. per minute with a delay of no more than 20 seconds, preferably less than 15 seconds, between application of the cooling treatment and exiting of the last hot rolling pass. The rate at which the material is cooled from 250 F. to room temperature is not critical, although for convenience the material is cooled directly to room temperature at a rate greater than 100 F. per minute. The magnesium silicide is thereby retained in solution thus eliminating the need for a flash solutionizing operation.

The solutionized redraw rod can then be cold drawn without an intermediate softening treatment in excess of 98% reduction in cross sectional area. This is in distinction to the present commercial process in which an upper limitation is applied to the amount of cold reduction after solutionizing. However, when aluminum alloy 6201 is utilized, it is necessary to apply at least 70% cold reduction, and preferably at least 75% cold reduction, before the final aging treatment.

Combinations of mechanical and electrical properties comparable or superior to those of present commercial material can be obtained at final diameter by the ap plication of an appropriate and conventional softening treatment consisting of holding at between 250 and 450 F. for 15 minutes minimum. Preferably this treatment should be conducted between 300 to 350 F. for 1 to 8 hours. Specification and mechanical and electrical properties are obtained using the above process with cold reduction after solutionizing from 70 to 99% reduction in area without intermediate softening treatments.

The present invention is amenable to use with any aluminum base alloy containing from 0.20 to 1.3% silicon and from 0.3 to 1.4% magnesium, with the 6201 alloy being preferred. Naturally, conventional impurities may be present and additives may be employed to achieve particular results. For example, the alloy may contain 1.0% iron max., 1.0% copper max., 0.8% manganese max., 0.35% chromium max., 0.5% zinc max., 0.001- 006% boron, 0.2% titanium max., and others each 0.05% max., total 0.15%. Boron is a particularly advantageous alloying addition.

The present invention will be more readily understandable from a consideration of the following illustrative examples.

ExampleI An alloy containing 0.72% magnesium, 0.68% silicon, 0.22% iron and 0.018% boron was horizontally DC cast to a diameter of 2%". The casting was reheated to around 750 F., held at that temperature for minutes and rolled to redraw rod in a ten-stand, continuous hot mill to a diameter of /5". The rod exited the rolling mill at 550 F. and was air cooled to room temperature. The resulting redraw rod had a coarse dispersion of Mg Si out of solution. The redraw rod was cold drawn 80% and aged for 4 hours at 325 F. Four samples of aged wire showed a low average tensile strength of around 35,000 p.s.i.

4 Example 11 The redraw rod of Example I was heated at 1025 F. for 10 minutes at temperature, total time in the furnace of 16 minutes, and then quenched in water without a de liberate intermediate delay. This served to solutionize the coarse Mg Si completely. The solutionized redraw rod was drawn and aged at 325 F. for 4 hours. Eight tensile samples of the wire showed a satisfactory average tensile strength of 48,000 p.s.i. This essentially duplicates present commercial processing.

Example IH The cast alloy bar of Example I was heated to 1025 F. and held at that temperature for 15 minutes5 hours. It was then rolled in a ten-stand tandem mill to redraw rod. The cast bar entered the rolling mill at 1025 F. and exited at 650 F. The average cooling rate during hot rolling was 1600 F./minute. The rod was then cooled to room temperature in still air at an average rate of around 10 F./minute. Examination of the microstructure showed a fine dispersion of precipitated Mg Si. The redraw rod was cold drawn 80% to 0.160" diameter and aged at 325 F. for 4 hours. Four samples of aged wire showed a low average tensile strength of around 35,000 p.s.i.

Example IV The cast bar of Example I was hot rolled according to the practice in Example III with an exit temperature of 650 -F. and an average cooling rate of 1600 F./ minute during hot rolling. The redraw rod exiting the hot mill was quenched in cold water to room temperature with no more than 2 seconds delay before entering the coolant. The cooling rate of the rod in the coolant was very high and was around 10,000 F/minute. The redraw rod so treated showed no significant precipitation of Mg Si in its microstructure. It was then drawn 80% to 0.160" diameter and aged at 325 F. for four hours. Eight samples of the wire showed a satisfactory average tensile strength of around 49,000 p.s.i., an average elongation of around 5% and an average electrical conductivity of around 54% IACS.

Example V A cast bar of Example I was hot rolled as shown in Example III. The redraw rod exited the hot mill at around 650 F. and had an average cooling rate of 1600 F./hour during hot rolling. The redraw rod was permitted to stand in still air for a period of 15 seconds before being quenched in water as in Example IV. The microstructure of the redraw rod showed barely detectable and occasional traces of Mg Si precipitate. The redraw rod was then drawn 80% to 0.160" diameter and aged at 325 F. for four hours. Four samples of the aged wire showed an average tensile strength of 48,000 p.s.i., an average elongation of 6% and an average electrical conductivity of 54% IACS.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. The process for preparing aluminum alloy conductors which comprises:

(A) providing an aluminum base alloy containing from 0.20 to 1.3% silicon, from 0.3 to 1.4% magnesium and the balance essentially aluminum;

(B) holding said alloy at a temperature of from 850 to 1150 F. for at least 5 minutes;

(C) hot rolling with a cooling rate during hot rolling of greater than F. per minute; and

(*D) cooling to below 250 F. at a rate greater than 100 F. per minute with less than 20 seconds delay between said cooling and said hot rolling.

2. A process according to claim 1 wherein said cooling in step (-D) at a rate greater than 100 F. per minute is to room temperature.

3. The process which comprises:

(A) providing an aluminum base alloy containing from 0.20 to 1.3% silicon, from 0.3 to 1.4% mag nesiurn and the balance essentially aluminum;

(B) holding said alloy at a temperature of from 850 to 1150 F. for at least 5 minutes;

(C) hot rolling to redraw rod with :a cooling rate during hot rolling of greater than 400 F. per minute;

(D) cooling the redraw rod to below 250 F. at a rate greater than 100 F. per minute with no more than 20 seconds delay between said cooling and said hot rollling;

(E) cold drawing with at least 70% reduction in cross sectional area; and

(F) heating at from 25-0 to 450 F. for at least 15 minutes.

4. A process according to claim 3 wherein said cooling in step (D) at a rate greater than 100 -F. per minute is to room temperature and wherein said delay between said cooling and said hot rolling is less than 15 seconds.

5. A process according to claim 4 wherein said holding step (B) is for from 15 minutes to 16 hours.

6. A process according to claim 4 wherein said holding step (B) is at a temperature of 900 to 1050 for from 15 minutes to 16 hours.

7. A process according to claim 4 wherein said redraw rod (C) has a diameter of about of an inch and is substantially free of precipitated magnesium silicide.

8. A process according to claim 4 wherein said cooled redraw rod (D) contains magnesium silicide substantially retained in solution.

9. A process according to claim 4 wherein said alloy is aluminum alloy 6201.

10. A process according to claim 4 wherein said heating step (F) is at 300 to 350 F. for from 1 to 8 hours.

11. A process according to claim 4 wherein said alloy (A) contains from 0.001 to 0.06% boron.

12. A process according to claim 4 wherein said alloy (A) contains 1.0% iron max., 1.0% copper max, 0.8% manganeses maX., 0.35% chromium max., 0.5% zinc max., 0.2% titanium max., and others each 0.05% max., total 0.15%.

References Cited UNITED STATES PATENTS 3,031,299 4/ 1962 Criner 14811.5 3,219,491 11/1965 Anderson et a1 l48-l1.5 3,234,053 2/1966 =Pryor 148-11.5 3,329,537 7/1967 Loach 148-121 L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 14811.5 

